1. Field of the Invention
This invention relates to a printed circuit board provided with alignment marks to be used for correcting, if necessary, the positions of the parts mounted on the substrate at the time of mounting them, a method of mounting parts on such a printed circuit board and a method of verifying each of the mounting positions of the parts mounted on such a printed circuit board.
2. Description of Related Art
It is a general practice that, when mounting parts such as semiconductor IC chips on the mounting surface of a printed circuit board, typically creamy solder is deposited on the mounting lands of the mounting surface of the printed circuit board by screen printing and, after mounting the parts on corresponding areas of the printed creamy solder, the entire printed circuit board is made to pass through a reflow furnace in order to heat and melt the solder and bond the parts to the corresponding lands by the solder.
When depositing creamy solder in the mounting process using the above described known method, the printing positions of creamy solder are corrected by referring to an alignment mark and also to substantially semicircular lands that have been arranged in advance on the mounting surface of the printed circuit board in order to minimize the positional errors of the printing positions of creamy solder so that solder may be deposited exactly at desired positions.
Additionally, when parts to be mounted are actually placed on the corresponding respective areas of the creamy solder that has been deposited by screen printing in the mounting process by means of the known method, the positions of the mounted parts are corrected by referring to the above described alignment mark in order to minimize the positional errors of the mounted parts.
With the above described method, a solder printing apparatus carries out the operation of correcting the areas of the creamy solder deposited by screen printing by referring to the alignment mark and a part mounting apparatus carries out the operation of correcting the positions of the mounted parts also by referring to the alignment mark. In other words, the two apparatus perform the respective position correcting operations separately by referring to a same single alignment mark that has been arranged in advance on the printed circuit board.
Therefore, if there arises an error of 180° in each of the position correcting operations that are equally performed by referring to the alignment marks, it may be impossible to mount the one or more than one part correctly on the respective areas of the creamy solder deposited by screen printing. Note that the above-cited position correcting method is described in Japanese Patent Application Laid-Open Publication No. 5-299794.
More specifically, referring to FIG. 1 of the accompanying drawings, if the position of the creamy solder 104 deposited on a mounting land 103 is corrected by referring to the alignment mark 102 arranged in advance on the mounting surface 101a of the printed circuit board 101 to consequently give rise to a positional error in the direction of arrow X in FIG. 1 to the creamy solder 104 deposited by screen printing and subsequently the position of the part 105 that is to be mounted on the creamy solder 104 deposited by screen printing by referring to the alignment mark is corrected to consequently give rise to a positional error in the direction opposite to the direction of X, it may be impossible to properly mount the part 105 on the creamy solder 104 that is deposited by screen printing.
In such a case, when the part 105 that is not aligned with the cream solder 104 is mounted on the printed circuit board 101 and the creamy solder 104 is heated and molten by means of a reflow soldering method, there will arise a problem of incorrect mounting position. The net result will be a low manufacturing yield.